We present here our based prism low resolution spectrograph baptized BESOS or BEst Simple Optical Spectrograph (kisses in spanish). Designed in 2003, the spectrograph was proposed to overcome the low throughput of our previous instrument LOROS (coming soon to this blog) which was an instrument based on an on-axis dispersion prism obtained from a commercial spectroscope. The total efficiency of LOROS was only 25% in the visible spectral range. BESOS was built with only two doublets and a prism. This configuration reached almost 87 % at 620 nm. With such efficiency and low resolution, we expected to measure the red shift of the most bright galaxies and quasars.
In this post we provide a description of the instrument, features, performances and the set of mechanical drawings.
The Figure below shows the optical design of BESOS. The description of the elements is given in the Table below. The prism works at the minimum deviation and for this configuration the incidence and refracted angle to the input and output prism surface is 59.6960º respectively.
Two LINOS (now Qioptiq) doublets were chosen as collimator and objective respectively. An equilateral 60º prism from Edmund Optics was used as disperser. The image quality at 400, 550 and 700 nm is illustrated in the following Figure. The square is 20 μm side. The images for these 3 wavelengths were optimized to have their minimum spot size perpendicular to the dispersion.
|Name||BESOS (BEst Simple Optical Spectrograph)|
|Description||Low resolution spectrograph based on an equilateral prism|
|Slit||Ni plate Ø 10 mm, 25 µm thick, centered slit:25 µm width, 2 mm long. Labelcomat (B)|
|Collimator||Doublet f = 30 mm, Ø 12.5 mm, external mount. Ø 25 mm. Linos ref. G052008000. Glass: SF18. Coated: ARB2 VIS|
|Prism||Dispersion prism. Material SF18, 15x15mm. AR coating. Edmund Scientific Ref U43-494|
|Objective||Doublet f = 40 mm, Ø 12.5 mm, external mount. Ø 25 mm. Linos ref. G052010000. Glass: SF18. Coated: ARB2 VIS|
|Telescope interface||Standard 1.25” tube.|
|Camera interfaces||T2 thread|
|Eye piece.||f = 20 mm, standard barrel Ø 1.25”, with extender15 mm, Ø 1.25” (included). For direct spectrum or slit observation|
|Slit illumination||Red LED, 10 mA.|
|Power supply||Battery 12 V Model MN21/A23/K23A/LRV08|
|Slit viewer lens||Doublet f = 30 mm, Ø 12.5 mm, external mount Ø 25 mm. Linos ref. 063130|
|Slit viewer interface||Internal tube standard Ø 1.25”|
|Total transmission (without CCD)||
|CCD test camera||SBIG ST-7 XMEI, KAF-0401E 756×510, 9×9µm|
|Dispersion||0.72 nm/pixel @ 650nm|
|Spectral range||362 nm – 812 nm|
All BESOS technical drawing ara available for download in this PDF document: BesosAllDrawings
This image describe the BESOS assembly with both optical and mechanical components. The only remark worth being mentioned is that the mechanical part 3 – Folding Mirror is made enterily of black anodized aluminium except the inclined surface that has been polished till it achieved the quality of a mirror surface (probably would habe been simpler solution to glue a small mirror).
The following photos show BESOS in different configurations
- Mallorca (Spain) .November 2003. All exposures between 1 and 120 seconds.
“BESOS: a prism spectrograph” by CAOS group is licensed under a Creative Commons Attribution-Non-Commercial-No Derivative Works 3.0 Germany License.
Based on a work at spectroscopy.wordpress.com.